Below is the average age when the baby teeth, primary teeth, come into a child's mouth highted in yellow.
Also when the adult teeth start to erupt into the child's mouth is when the baby teeth are lost.
Note, the first adult molars erupt about 6 years old, no baby teeth are lost for these to erupt so many times parents think these are more baby teeth in the very back of the mouth but these are adult teeth.
So help your child brush all the way to the very back of the mouth to help prevent cavities in the first adult teeth your child will have.